1. Field of the Invention
The present invention involves threaded tubular joints usable in oil and gas well drilling and production, such as tubing, casing, line pipe, and drill pipe, commonly known collectively as oilfield tubular goods. More particularly, the invention relates to a tubular joint for connecting male pin and female box members.
2. Background Art
The use of threaded tubular connections for joining flow conduits in an end-to-end relationship to form a continuous flow path for transporting fluid under pressure is well known. Oilfield tubular goods all use threaded connections for connecting adjacent sections of conduit or pipe. Examples of such threaded end connections designed for use on oilfield tubular goods are disclosed in U.S. Pat. Nos. 2,239,942; 2,992,019; 3,359,013; RE 30,647; and RE 34,467, all of which are assigned to the assignee of the present invention.
In U.S. Pat. No. RE 30,647 by Blose, a particular thread form or structure is disclosed for a tubular connection that provides an unusually strong joint while controlling the stress and strain in connected pin and box members within acceptable levels. The pin member is equipped with at least one generally dovetail-shaped external thread whose width increases in one axial direction along the pin, while the box member is equipped with at least one matching generally dovetail-shaped internal thread whose width increases in the other axial direction. In this manner, the mating set of helical threads provide a wedge-like engagement of opposing pin and box flanks that limit the extent of relative rotation between the pin and box members, and define a forcible make-up condition that completes the connection. In this thread structure, the flank shoulder angles as well as the thread width can be used to control the stress and strain preload conditions induced in the pin and box members for a given make-up torque. Thus, by tailoring the thread structure to a particular application or use, the tubular connection or joint is limited only by the properties of the materials selected.
As shown in FIG. 1, a prior art connection 10 includes a pin member 11 and a box member 12. Box member 12 has a tapered, internal, generally dovetail-shaped thread structure 14 formed thereon and adapted for engaging complementary tapered, external, generally dovetail-shaped thread structure 15 formed on pin member 11 to mechanically secure the box and pin members in a releasable manner.
Internal thread 14 of box member 12 has stab flanks 18, load flanks 16, roots 20, and crests 24. The thread increases in width progressively at a uniform rate in one axial direction substantially the entire helical length of thread 14. External thread 15 of pin member 11 has stab flanks 19, load flanks 17, roots 21, and crests 25. The thread increases in width progressively at a uniform rate in the other axial direction substantially the entire helical length of thread 15. The oppositely increasing thread widths and the taper of threads 14 and 15 cause the complementary roots and crests of the respective threads to move into engagement during make-up of the connection followed by movement of complementary stab and load flanks into engagement upon make-up of the connection.
The pin member 11 or the box member 12 defines the longitudinal axis 13 of the made-up connection 10. The roots and crests of the box and pin members are flat and parallel to the longitudinal axis of the connection and have sufficient width to prevent any permanent deformation of the threads when the connection is made up.
The conventional connection 110 illustrated in FIG. 9 is provided with a multiple or two step cylindrical thread having a stop shoulder 130 formed on the pin member 111 that engages a corresponding stop shoulder 132 on the box 112.
In general, in accordance with one or more embodiments, the present invention is a threaded tubular connection including a box member having an internal thread, a pin member having an external thread engageable with the internal thread of the box member, and a protruding sealing surface disposed in the box member such that the pin member flexes radially inward upon passing the protruding sealing surface during make-up. The threaded tubular connection also includes a recessed seal cavity disposed in the box member, and a reverse angle shoulder at the pin nose that forces the pin member to flex radially outward into the recessed seal cavity of the box member upon final make-up.
In general, in accordance with one or more embodiments, the present invention is a method of forming a double flex seal for a tubular connection that includes engaging an external thread of a pin member with an internal thread of a box member and flexing a pin nose of the pin member radially inward by passing the pin nose over a protruding sealing surface of the box member during make-up. The method also includes flexing the pin nose radially outward when a reverse angle shoulder of the pin nose comes into contact with a reverse angle shoulder of the box member during make-up and completing the double flex seal by finally making up the connection such that the pin nose of the pin member seats in a recessed seal cavity disposed in the box member.
In general, in accordance with one or more embodiments, the present invention is a threaded tubular connection including a box member having an internal thread and a pin member having an external thread engageable with the internal thread of the box member. The threaded tubular connection also including means for flexing the pin member radially inward during make-up, means for engaging the pin member and the box member such that the pin member flexes radially outward upon final make-up, and means for forming a seal between the pin member and the box member.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.